[refactor] make set_attention_slice recursive (#1532)
* make attn slice recursive
* remove set_attention_slice from blocks
* fix copies
* make enable_attention_slicing base class method of DiffusionPipeline
* fix set_attention_slice
* fix set_attention_slice
* fix copies
* add tests
* up
* up
* up
* update
* up
* uP
Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>
